👤 Fred S Lamb

Postprandial metabolic impairments play a key role in the pathophysiology of cardiometabolic diseases. While liver fat content has been linked to distinct fasting metabolite profiles, its relationship with postprandial metabolite profiles remains unexplored. In this study, we aimed to (1) examine to what extent liver fat content is associated with the postprandial metabolomic profile beyond fasting metabolites; and (2) investigate whether diet-induced changes in liver fat content are associated with changes in plasma metabolites identified in objective 1. In a subpopulation (n = 1986) of an existing cohort study and a 12-week dietary intervention study (n = 80), liver fat content was measured by proton magnetic resonance spectroscopy and categorized as low (< 2.5%), middle (2.5-5.5%), or high (> 5.5%). In the cohort study, plasma metabolomic profiles were quantified by NMR spectroscopy at fasting (T High liver fat group was characterized by higher fasting and postprandial levels of triglycerides, all VLDL and the small LDL/HDL subclasses, ApoB, fatty acids, glycoprotein acetyls, and BCAAs, and lower medium/larger HDL subclasses, and acetate compared to the low liver fat group. In the high vs. low liver fat group, postprandial responses of cholesterol content of S-LDL, IDL, and S-HDL, glutamine and histidine, omega-3% and DHA % were lower. Diet-induced reductions in liver fat were associated with reductions in 40 fasting plasma metabolites, including VLDL-TG, tyrosine, isoleucine, fatty acid ratios, and most of the VLDL subclasses. Postprandial metabolomic profiling revealed additional associations between liver fat content and plasma metabolites beyond fasting measures, particularly in lipoprotein cholesterol and fatty acid composition. Diet-induced reductions in liver fat were associated with favorable changes in fasting metabolites, but not postprandial metabolite responses. Future studies with harmonized postprandial assessment are needed to further elucidate the postprandial observations and the underlying mechanisms. The trials in this study were registered at clinicaltrials.gov as NL21981.058.08/P08.109 and NCT02194504. Show less

The APOE genotype influences metabolic and neurodegenerative outcomes, with APOE4 carriers at higher risk for Alzheimer's disease (AD) and metabolic dysfunction. This study examines how long-term dietary interventions affect systemic metabolism, retinal structure/ function in APOE3-knock-in (KI, neutral for AD) and APOE4-KI mice. Humanized APOE3 and APOE4-KI mice received either a control diet (CD) or a Western diet (WD) for 2, 6, or 12 months. Body weight, glucose metabolism, lipid profiles, retinal structure, function, vasculature, visual performance, and inflammatory markers were analyzed. WD induced early glucose intolerance in APOE4 mice (2 months); APOE3 mice showed impairment only after prolonged exposure (6-12 months). Notably, WD-fed APOE3 mice exhibited more pronounced hyperlipidemia than APOE4 mice. APOE4 CD mice displayed early retinal thinning (6 months), while APOE4 WD mice initially exhibited retinal swelling, followed by degeneration (12 months). WD exacerbated retinal vascular dysfunction in APOE4 mice, with increased tortuosity and reduced vascular area. Elevated Il1b expression in WD-fed APOE4 mice confirmed inflammation-associated retinal dysfunction. APOE4 mice showed heightened dietary vulnerability, with WD worsening metabolic, retinal, and vascular impairments. While CD showed better glucose tolerance, it did not prevent retinal dysfunction. These findings underscore the need for genotype-specific dietary strategies to mitigate APOE4-associated risks. Show less

Alzheimer's disease (AD), particularly late-onset AD (LOAD), affects millions worldwide, with the apolipoprotein ε4 (APOE4) allele being a significant genetic risk factor. Retinal abnormalities are a hallmark of LOAD, and our recent study demonstrated significant age-related retinal impairments in APOE4-knock-in (KI) mice, highlighting that retinal impairments occur before the onset of cognitive decline in these mice. Müller cells (MCs), key retinal glia, are vital for retinal health, and their dysfunction may contribute to retinal impairments seen in AD. MCs maintain potassium balance via specialized inwardly rectifying K Show less

In response to extracellular ligands, G protein-coupled receptors (GPCRs) undergo conformational changes that induce coupling to intracellular effectors such as heterotrimeric G proteins that trigger various downstream signaling pathways. These events have been shown to be highly regulated by concerted effects of post-translational modifications (PTMs) that occur in a ligand-dependent manner. Most notably, phosphorylation of residues in the C-terminal cytoplasmic tail of GPCRs has been strongly implicated in promoting receptor interactions with β-arrestins (βarrs), which are cytosolic adaptor proteins that modulate G protein coupling, receptor internalization, and perhaps also serve as signaling modules in their own right. Here, we use proteomic methods to identify C-tail residues that are phosphorylated in the glucagon family of class B1 GPCRs (GLP-1R, GCGR, and GIPR) upon agonist addition. We demonstrate that the phosphorylation of GLP-1R and GIPR is a critical determinant in the formation of GPCR-βarr complexes. However, our results suggest that ligand-induced βarr recruitment to GCGR proceeds in a phosphorylation-independent manner. These findings highlight the importance of recognizing phosphorylation as a component in the regulation of class B1 GPCR signaling but also the need to consider how such phenomena may not necessarily yield identical effects on intracellular signaling cascades. Show less

Leucine Rich Repeat Containing 8A (LRRC8A) anion channels (VRACs) associate with NADPH oxidase 1 (Nox1) and support extracellular superoxide (O We assayed O KO cells were less permeable to extracellular O Loss of LRRC8A reduced O Show less

The heterochromatin protein 1 (HP1) sub-family of CBX chromodomains are responsible for the recognition of histone H3 lysine 9 tri-methyl (H3K9me3)-marked nucleosomal substrates through binding of the N-terminal chromodomain. These HP1 proteins, namely, CBX1 (HP1β), CBX3 (HP1γ), and CBX5 (HP1α), are commonly associated with regions of pericentric heterochromatin, but recent literature studies suggest that regulation by these proteins is likely more dynamic and includes other loci. Importantly, there are no chemical tools toward HP1 chromodomains to spatiotemporally explore the effects of HP1-mediated processes, underscoring the need for novel HP1 chemical probes. Here, we report the discovery of HP1 targeting peptidomimetic compounds, UNC7047 and UNC7560, and a biotinylated derivative tool compound, UNC7565. These compounds represent an important milestone, as they possess nanomolar affinity for the CBX5 chromodomain by isothermal titration calorimetry (ITC) and bind HP1-containing complexes in cell lysates. These chemical tools provide a starting point for further optimization and the study of CBX5-mediated processes. Show less

Cholesteryl ester transfer protein (CETP) is mainly expressed by Kupffer cells in the liver. A reduction of hepatic triglyceride content (HTGC) by pioglitazone or caloric restriction is accompanied by a decrease in circulating CETP. Since GLP-1 analogues also reduce HTGC, we assessed whether liraglutide decreases CETP. Furthermore, we investigated the association between HTGC and CETP in a population-based cohort. In a placebo-controlled trial, 50 patients with type 2 diabetes were randomly assigned to treatment with liraglutide or placebo added to standard care. In this trial and in 1,611 participants of the Netherlands Epidemiology of Obesity (NEO) study, we measured HTGC and circulating CETP by proton magnetic resonance spectroscopy and ELISA, respectively. The HTGC was decreased in the liraglutide group (-6.3%; 95%CI of difference [-9.5, -3.0]) but also in the placebo group (-4.0%; 95%CI[-6.0, -2.0]), without between-group differences. CETP was not decreased by liraglutide (-0.05 µg/mL; 95%CI[-0.13, 0.04]) or placebo (-0.04 µg/mL; 95%CI[-0.12, 0.04]). No association was present between HTGC and CETP at baseline (β: 0.002 µg/mL per %TG, 95%CI[-0.005, 0.009]) and between the changes after treatment with liraglutide (β: 0.003 µg/mL per %TG, 95%CI[-0.010, 0.017]) or placebo (β: 0.006 µg/mL per %TG, 95%CI[-0.012,0.024]). Also, in the cohort n o association between HTGC and CETP was present (β: -0.001 µg/mL per SD TG, 95%CI[-0.005, 0.003]). A reduction of HTGC after treatment with liraglutide or placebo does not decrease circulating CETP. Also, no association between HTGC and CETP was present in a large cohort. These findings indicate that circulating CETP is not determined by HTGC.Clinical Trial Registration: Clinicaltrials.gov (NCT01761318). Show less